Hormone-directed Transport of Assimilates in Decapitated Internodes of Phaseolus vulgaris L.

Application of ethylene, indole-3yl-acetic acid (IAA), 6-(benzylamino)-9-(2tetrahydropyranyl)-9-Hpurine (SD8339), or mixtures of IAA, gibberellic acid (GA),and cytokinins, increased the accumulation of ¹⁴C-activity indecapitated internodes of Phaseolus vulgaris seedlings. Differencesbetween treated and untreated tissues with respect to importof labelled assimilate were detected 3 h after application ofa mixture of IAA, GA, and SD8₃₃₉. In longer-term experimentseffects of the growth-regulator mixture on translocation oflabel were greater than those of IAA alone. Inhibitory effectsof abscisic acid on import of assimilate were counteracted bySD8₃₃₉. The ability of internode tissues to import ¹⁴C-photosynthatedeclines with time from decapitation, and a decrease in incorporationof ¹⁴C-leucine into protein was detected after 24 h. There wasan increase in protein and RNA synthesis in internodal tissuesfollowing a 2.5-h pre-treatment of decapitated internodes withIAA, GA, and SD8₃₃₉. Concentrations of 2, 3, 5-triiodobenzoicacid which inhibit ¹⁴C-IAA translocation stimulate protein synthesisin decapitated internodes, and augment the IAA-effect on importof ¹⁴C-photosynthate. ‘Hormone-directed’ assimilatetransport is discussed in relation to confounding effects ofgrowth responses and differential senescence of treated anduntreated tissues. It is suggested that accumulation of labelledassimilate in treated tissues results from effects of growthregulators on synthetic activities at the point of application.